Critical maintenances you can do yourself! (Always flip the AC breaker on the electrical panel off or pull the diconnect beforehand):
Rinsing the AC coil will clean away all debris and dust on the coils which will allow the unit to more effeciently transfer heat into and out of your home and will also increase air flow.
Replacing air filters will increase air flow providing a much better cooling experience and will also increase the life span of your unit.
Replacing/repairing the thermostat if the set temperature isn't accurate will prevent any miscommunication between your thermostat and your AC unit.